Conventional silica-based aerogels are among the most promising materials given their special properties, such as extremely low thermal conductivity (~15 mW/mK) and low-density (~0.003 - 0.5 g/cm³) as well as high surface area (500 - 1200 m²/g). However, they indeed lack in mechanical properties and endure extensive and energy-consuming processing steps. Silica-based aerogels are mostly fragile and possess minimal mechanical properties as well as a long processing procedure which hinders their application range. The key point in improving the mechanical properties of such a material is to increase the connectivity in the aerogel backbone through eliminating typical particulate morphology as it suffers from a weak connection links between particles. By optimizing the material composition and processing conditions of materials, the aerogel can be tailored with different functional capabilities and morphology. However, tailoring process of the silica-based aerogels experiences several challenges such as low integrity of the solid part, lack of extensive void fraction, and shrinkage during the gelation and drying process, which are mostly unavoidable when making aerogels. The main two challenges of failed tailoring practices are:​ (I) the lack of strong solid backbone throughout a monolithic aerogels with strong mechanical properties while preserving their unique features, and (II) the lack of deep understanding of the sol-gel process of polymeric silica-based precursor with and without carbonic fillers.

Recently, graphene nanoplatelets (GnPs) have attracted a great deal of attention as a multifunctional reinforcing nanofiller in polymer composites, which is due to their unique twodimensional honeycomb layer structure, their excellent mechanical properties and their isotropic reinforcement capability in more than one direction. Here, the effect of the spinodal decomposition process in creating a nonparticulate morphology in the GnPs' orientation and dispersion is investigated. It is also studied how the gelation reaction can participate in the inclusion of GnPs in the aerogel backbone during the sol-gel process to strengthen the body of the gel. Meanwhile, the process of GnP exfoliation and restacking elimination during sol-gel transition is comprehensively studied. The present thesis also analyzes the gelation kinetics and thermodynamics in the presence of GnP and graphene oxide (GO) using in-situ rheology, light scattering (DLS), small-angle X-ray scattering (SAXS) and pore-structure-analyzer. The data collected during the gel network formation obtained with and without GnP or GO are analyzed in which to fully study the kinetics of structure evolution during the gelation. It is confirmed that the use of spinodal decomposition to create a nonparticulate gel network helps to offset the required long aging step during the solgel process, which is inevitable to strengthen the particle-to-particle neck using conventional methods such as nucleation and growth. It is also verified that this gelation technique enables the system to take advantage of GnP's full potential through correct exfoliation and elimination of restacking and re-agglomeration.

This current work addressed both those aforementioned challenges to have a deep understanding of hybrid polymer-based silica aerogels reinforcement and techniques to integrate them into many sectors. The synthesis process focused mostly on hybrid carbon-modified polymeric silica-based aerogels. The micromorphological parameters were studied to quantify each parameter that controlled the assembly of the aerogel three-dimensional network with and without carbonic fillers. Then, each parameter was correlated the structural final property to better understand the origin of the uniqueness of the aerogel’s features.

The carbon-modified polymeric silica-based aerogels were first modified to enhance their mechanical properties by the addition of flexible nanofibers and stiff nanosheets into the structurer. The composites assembled homogeneously into the carbon-modified polymeric silica-based aerogel structure to create a uniform network of the solid struts along with the backbone. With such network, the mechanical properties of the aerogels increased dramatically while preserving/advancing their unique features such as high surface area and thermal stability. The new aerogels could operate a high temperature with high surface area. Furthermore, such material could resist moisture, which makes this material ideal to be used in high temperature and humid environments